A fourteen year old boy with Rubinstein-Taybi-syndrome presented with a severe congenital subvalvular fibrous aortic stenosis with associated aortic regurgitation. Transthoracic echocardiographic imaging and left heart angiography showed a transvalvular peak systolic pressure gradient of 90 mmHg and a regurgitant fraction of 30%. The surgical treatment consisted of resection of the subvalvular fibrous tissue and subsequent aortic valvuloplasty. Intraoperative transesophageal echocardiography revealed a wide systolic opening of the aortic valve and good coaptation of the aortic valve leaflets in diastole. Two-dimensional color-coded and contrast echocardiography were successfully used to confirm a satisfactory reconstruction. Transesophageal echocardiography therefore represents a valuable tool in the assessment of the morphologic and haemodynamic status, especially in rare cases of congenital heart disease in older children.